(a) Fields of the Invention
The present invention relates to semiconductor laser devices. In particular, the present invention relates to semiconductor lasers which can emit light ranging from red to infrared and which are employed for light sources for pickups of optical disk devices, or light sources for other electronic devices and information-processing devices.
(b) Description of Related Art
At present, digital video disks (DVD) capable of high-density packing of information and mass storage and DVD drive devices for record and playback of the information therein are commercially available, and they receive attention as products whose demand will be further growing in the future. In order to provide high-density recording of information, the DVD uses, as a laser source for record and playback, an AlGaInP-based semiconductor laser with an emission wavelength of 650 nm. Thus, in the conventional DVD drive device, an optical pickup cannot play back information in a compact disk (CD) or a MiniDisc (MD) which uses for playback an AlGaAs-based semiconductor laser with an emission wavelength of 780 nm.
To address this disadvantage, an optical pickup is employed in which an AlGaInP-based semiconductor laser with an emission wavelength range of 650 nm and an AlGaAs-based semiconductor laser with an emission wavelength range of 780 nm are separately incorporated as laser chips into respective packages to mount the two lasers with different wavelengths therein. This provides a drive device capable of playing back information in any of DVDs, CDs, and MDs.
However, since the optical pickup as described above mounts the two packages composed of the AlGaInP-based semiconductor laser and the AlGaAs-based semiconductor laser, respectively, it has an increased size. Thus, a DVD drive device having such an optical pickup employed therein also has an increased size.
In contrast to this, an integrated semiconductor light-emitting device as disclosed in Japanese Unexamined Patent Publication No. H11-186651 is known which has light emission structures composed of semiconductor layers grown on a single substrate, respectively, and which has multiple types of semiconductor light-emitting elements with different emission wavelengths.
One example of the conventional integrated semiconductor light-emitting device thus constructed is shown in FIG. 9. Referring to FIG. 9, in the conventional integrated semiconductor laser device 100, on a single n-type GaAs substrate 101, an AlGaAs-based semiconductor laser LD1 with an emission wavelength range of 700 nm (for example, 780 nm) and an AlGaInP-based semiconductor laser LD2 with an emission wavelength range of 600 nm (for example, 650 nm) are integrated to be separated from each other.
In this structure, as the n-type GaAs substrate 101, use is made of, for example, a substrate having an orientation of (100) plane or using as a principal plane a surface, for example, 5 to 15° inclined from the (100) plane.
In the AlGaAs-based semiconductor laser LD1, on the n-type GaAs substrate 101, an n-type GaAs buffer layer 111, an n-type AlGaAs cladding layer 112, an active layer 113 with a single quantum well (SQW) structure or a multiple quantum well (MQW) structure, a p-type AlGaAs cladding layer 114, and a p-type GaAs cap layer 115 are sequentially stacked in this order from bottom to top.
The upper portion of the p-type AlGaAs cladding layer 114 and the p-type GaAs cap layer 115 are formed in a striped pattern extending in one direction. Both side parts of the striped portion are provided with n-type GaAs current narrowing layers 116, respectively, and they form a current narrowing structure. A p-side electrode 117 is provided on the p-type GaAs cap layer 115 in a striped pattern and the n-type GaAs current narrowing layer 116, and is in ohmic contact with the p-type GaAs cap layer 115. As the p-side electrode 117, for example, a Ti/Pt/Au electrode is used.
On the other hand, in the AlGaInP-based semiconductor laser LD2, on the n-type GaAs substrate 101, an n-type GaAs buffer layer 121, an n-type AlGaInP cladding layer 122, an active layer 123 with a SQW structure or a MQW structure, a p-type AlGaInP cladding layer 124, a p-type GaInP intermediate layer 125, and a p-type GaAs cap layer 126 are sequentially stacked in this order from bottom to top.
The upper portion of the p-type AlGaInP cladding layer 124, the p-type GaInP intermediate layer 125, and the p-type GaAs cap layer 126 are formed in a striped pattern extending in one direction. Both side parts of the striped portion are provided with n-type GaAs current narrowing layers 127, respectively, and they form a current narrowing structure. A p-side electrode 128 is provided on the p-type GaAs cap layer 126 in a striped pattern and the n-type GaAs current narrowing layer 127, and is in ohmic contact with the p-type GaAs cap layer 126. As the p-side electrode 128, for example, a Ti/Pt/Au electrode is used.
On the back surface of the n-type GaAs substrate 101, an n-side electrode 129 is provided to be in ohmic contact with the n-type GaAs substrate 101. As the n-side electrode 129, for example, an AuGe/Ni electrode or an In electrode is used.
The p-side electrode 117 of the AlGaAs-based semiconductor laser LD1 and the p-side electrode 128 of the AlGaInP-based semiconductor laser LD2 are soldered on a heat sink H1 and a heat sink H2, respectively, which are provided on a package base 200 to be electrically separated from each other.
With the conventional integrated semiconductor laser device 100 constructed as shown above, a current can be passed between the p-side electrode 117 and the n-side electrode 129 to drive the AlGaAs-based semiconductor laser LD1. Likewise, a current can be passed between the p-side electrode 128 and the n-side electrode 129 to drive the AlGaInP-based semiconductor laser LD2. Then, by driving the AlGaAs-based semiconductor laser LD1, a laser light with a wavelength range of 700 nm (for example, 780 nm) can be taken therefrom, and by driving the AlGaInP-based semiconductor laser LD2, a laser light with a wavelength range of 600 nm (for example, 650 nm) can be taken therefrom. Which of the AlGaAs-based semiconductor laser LD1 and the AlGaInP-based semiconductor laser LD2 is driven is switch-selectable with an external switch.
As described above, since the conventional integrated semiconductor laser device 100 has the AlGaAs-based semiconductor laser LD1 with an emission wavelength range of 700 nm and the AlGaInP-based semiconductor laser LD2 with an emission wavelength range of 600 nm, a laser light targeted for DVDs and a laser light targeted for CDs and MDs can be picked up independently. Therefore, by mounting the integrated semiconductor laser device 100 as a laser source on an optical pickup of a DVD drive device, it can record and play back information in any of DVDs, CDs, and MDs.
Since the AlGaAs-based semiconductor laser LD1 and the AlGaInP-based semiconductor laser LD2 have laser structures formed of the semiconductor layers grown on the single n-type GaAs substrate 101, the resulting integrated semiconductor laser device requires only one package. This downsizes the optical pickup and in turn downsizes the DVD drive device.